The present invention relates to a blending apparatus and method therefor. The apparatus and method will be described with respect to the blending of petroleum products but is applicable to the blending of other liquid or fluent materials such as, for example, food ingredients and the word "component" should be interpreted to include these materials.
1. Field of the Invention
When it is desired to produce a blended product from a number of components there are basically two ways of carrying out the blending operation. Firstly, a batch blending method passes measured quantities of component into, for example, a tank and then mixes them and when the mixing is completed the blended product is passed to a storage tank. The measuring of the various components can be carried out in a number of ways, for example in the case of liquid components by means of valves which may measure volume. In modern arrangements, however, the gathering of the component materials is often carried out by means of robots. Such an apparatus and method has considerable use particularly where relatively small quantities of blended product are to be produced.
In an alternative arrangement, the blended product may be produced by a method known a "in-line" blending in which the components are passed to a single line and are added to that line in a metered manner in accordance with their relative proportions in the final blended product. Such an in-line blending process is widely used and although not restricted thereto is particularly desirable when large quantities of blended products are to be produced.
The same apparatus may be used to produce different blended products by blending different components or by blending the same components in different proportions.
2. Description of the Prior Art
FIG. 1 illustrates diagrammatically a plan view of a typical installation for in-line blending. In this the components A to F from which the blended products are to be produced are stored separately in respective tanks 10A to 10F. Each tank 10A to F is connected by a respective pipeline 11A to F, via a stop valve 12A to F, a pump 13A to F (which may be a positive displacement pump), a flow meter 14A to F (which may be a turbine flow meter), and a check valve 15A to F, to an injection point 17A to F in a pipeline called a "blend header" 16 having an outlet 20 for the blended product. Control apparatus is provided to operate the pumps 13A to F in accordance with a predetermined relation which in general terms will be in proportion to the desired relative proportions of the components in the blended product. The rate of addition of the particular component is measured by means of the flow meter 14A to F which can in turn control the pump 13A to F. Clearly such an arrangement can be used to produce a wide variety of blended products by varying the porportion of components added from zero upwards. Thus, for example, in one application it may only be required to blend components A, B and C from tanks 10A, B and C in which case valves 11D, E and F can be closed. Furthermore, by means of a hose exchange 18A (not shown in FIG. 1 but situated between stop valves 12 and pumps 13) an individual pump 13A may be connected to different tanks at different times so that there is no need to have a dedicated pump 13 and meter 14 for each component tank.
FIG. 2 shows one of the lines 11A between a hose exchange 18A and the blend header 16 in more detail. FIG. 2 illustrates the hose exchange 18A already referred to, a further isolating valve 19A, a strainer 21A, the positive displacement pump 13A, an air eliminator 22A, the meter 14A and the check valve 15A. In prior arangements these have generally been arranged in a generally horizontal configuration and it will be noted in particular that the strainer 21A and air eliminator 22A by virtue of their design have sumps below the level of the line 11A. The strainer 21A protects the downstream pump and meter, and the air eliminator 22A ensures disposal of air "slugs" and being the highest point in the metering stream the normal vent is converted to allow blowback of the unmetered liquid back to storage.
The above described arrangement has been well known for a number of years and has worked quite effectively. However, there have been a number of problems with such an arrangement. The primary problem is that when a different component is attached to the hose exchange 18 the earlier component which is already in the line 11A, the strainer 21, the pump 13, the air eliminator 22 and the meter 14 will now be considered to be a contaminant since it will not be required in the new blended product. This means that the initial quantity of blended product which is produced after a different component is attached to the hose exchange 18 must be discarded or considered to be contaminated.
One of the most popular ways to remove as much as possible of the old component from the line 11A before the new component is passed to the hose exchange 18 has been to isolate check valve 15A by closing a closure valve (not shown) associated with check valve 15A and to pass air into the system via the air eliminator 22A to try to blow the old component back through the various parts to the hose exchange 18 and hence back to its relevant tank before disconnecting the hose exchange. In practice, however, it has been found that quite a lot of the original component remains.
Furthermore, using the hose exchange 18A is very labour intensive and far from foolproof unless some complicated electronic identification means is incorporated.